Ski boots conventionally comprise an outer rigid plastic shell, a leg portion journalled to the outer sides of the shell, and an inner liner, fully contained within the shell and adapted to comfortably receive the foot of the user. However, besides the need of comfortably housing the foot of the user, there is another need to be fulfilled, namely that of the transmission of the commands from the user's leg and foot to the ski during the sport practice, which must be as precise and quick as possible, whereby a very thick padding in the liner is not an acceptable solution.
Thus, a liner having a padding customized to the user's foot is a long felt need and a number of proposals were made in the past aiming to customize the ski boot to the user's foot by means of a formable liner, particularly a thermally formable liner.
According to a currently used technique, the liner is placed in the boot and heated by a hot air gun. Once heated, the user inserts his foot and tightens the boot, whereupon the liner is moulded to the shape of the foot and sets its shape as it cools.
This procedure requires heat to be applied until the liner reaches the appropriate temperature, and often an excessive heat is applied, leading to discomfort or worse for the user.
Moreover the liner will typically be thicker in some places, for example over the ankle bone, than in others, like e.g. over the instep. Consequently, excessive heat may be applied to the foot at the thinner parts of the liner.
It is also known to use electrically heated elements in moulding padding inserts in ski boots, as for example disclosed in U.S. Pat. No. 6,003,248.
However, the electrical heating arrangements proposed hitherto have a number of disadvantages, since they use relatively complex constructions with wires or ribbon conductors laminated to carrier films, and the distribution of the heat is not satisfactory and the resistance heating elements are relatively localised.
Another problem especially important for the ski boots is that often the inner liner becomes moistened during the use, causing discomfort for the user; moreover it would be preferable to have the inner liner dried after the use, before the ski boots are put aside for the next occasion of use. Likewise, in some cases, it would be preferable to have the inner liner slightly heated before the use.
Of course both the drying and the heating must be consistent with the places wherein the boots are used, such as for instance the ski fields, where some difficulties would exist in having proper facilities for providing electrical power of suitable characteristics.